Optical glass



United States Patent 2,996,393 OPTICAL GLASS Heinz Briimer, Hermannstein, and Norbert Meinert, Wetzlar (Lahn), Germany, assignors to Ernst Leitz, G.m.b.H., Wetzlar (Lahn), Germany, a corporation of Germany No Drawing. Filed Aug. 20, 1959, Ser. No. 834,954 Claims priority, application Germany Sept. 24, 1958 9 Claims. (Cl. 106-47) Our invention relates to optical glasses with a small dispersion in relation to their refractive index.

Glasses in this optical range are known and indeed obtained by melting down mixtures which contain a considerable amount of oxides of the rare earths. Also compositions are known which contain considerable amounts of barium oxide or strontium oxide or both and with which boric oxide or silica or both are used as glass formers. I

We have discovered that the amount of barium oxide or strontium oxide or both can be considerably decreased upon the addition of zinc especially as zinc borate. Through the decrease of the barium oxide content of the glass, according to our invention, the glasses are more stable chemically without change in the optical values.

To .these glasses oxides of magnesium and calcium as well as zirconium oxide and silica may be added. We have found it useful to select a content of barium borate between 5% and 45% by weight, and zinc borate between 20% and by weight. A further addition of zinc oxide permits less than 5% by weight of magnesium oxide and/ or less than 18% by weight of calcium oxide, less than 7.5% by weight of zirconium oxide and of silica less than 10% by weight. For controlling the index of refraction tungsten oxide below 5% by weight and lead oxide below 10% by weight can be used. To stabilize the glasses further an amount of aluminum oxide up to 10% maybe used. Instead of tungsten tantalum oxide or niobium oxide or both may be substituted in whole or in part. The zinc may be substituted in part by cadmium.

In the follownig Table 1 is shown first that a substitution of barium borate by zinc borate leaves the optical values unchanged.

Patented Aug. 15, 1961 Table 2 in percent by weight Melt NO. B80302): Z11(BOz)2 ZIOz Slog 71 v BIIIV/30-- 72. 8 24. 7 2. 5 1. 669 53. 7 Br/IV/31- 71. 0 24. 1 4. 9 1. 676 52. 6 Br/IV/35 60. 5 32. 8 6. 7 1. 6777 51. 6 Br/IV/36- 55. 5 30. 1 11. 8 2. 6 1. 690 BI/IV/33 53. 0 36. 0 11. 0 1. 672 51. 6

In the glasses of Table 3, either barium oxide and zinc oxide are added as borates. Additionally there are added to the mixture substantial amounts of zinc oxide and silica as well as zirconium oxide for stabilizing. With the aid of a further addition of lead oxide-obviously tungsten, tantalum and/or niobium could be used-the indices of refraction of the glasses thereby obtained are further increased. These glasses free from rare earth metal compounds already extend into the region which are known in the literature under the name lanthanum-flint type of glasses. The sum of borates of barium and zinc lies between and 80% by weight in which not more than 25% by weight of barium borate is used. The additional insertion of zinc oxide portion does not exceed 15% by weight. Silica is less than 15% by weight and zirconium oxide content is less than 8% by weight of the mixture. The lead oxide content can be present up to 20% by weight. Instead of zinc oxide cadmium oxide can also be used. To control the index of refraction and dispersion tungsten oxide and/or tantalum oxide and/or niobium oxide find application.

Table 3 in percent by weight Melt No. B8,(BO2)2 2110302), ZnO 610, 210; PbO n. v.

Burn/1--- 20. 4 46. 0 12. 4 13. 7 7. 5 1. 667 40. 7 Br/III/2- 19. 7 44. 5 11. 9 13. a 7. 3 3. 3 1. 673 43. 2 Burn 3-- 19. 1 43. 1 11.6 12. s 7. 0 6. 4 1.680 46. 6 Br/III/4 1s. 5 41. 7 11. 2 12. 4 6. 9 9. 3 1. 691 44. s Br/III/5 18.0 40.5 10.9 12.0 6.6 12.0 1.698 43.8 Br/III/6 16. 6 37. 5 10. 1 11. 2 6. 1 18.5 1. 706 41. 2

Table 1 in percent by weight 5 I In Table 4 there are further examples of mlxture add1- Me1tN0- 0 ZIKBOQI Zrofl 5102 tions with barium and zinc as borates together with fur- 1 658 54 6 ther addition of zinc oxide and/or cadmium oxide. For 74.7 25.3 gi l i 72.0 28.0 1.658 52.3 stabilizing again there are added to the mixture 1n part 9 5 gi $201; 2. 113 I: 223 54.6 zlrcomum oxide and silica. In one example the barlum fi l} 22:2 2%; {22? 22 3 borate is substituted in part by calcium borate.

'Table 4' in percent by weight Ba(BO)g- 5 50. o 44. s Z11(B0z)2-.. 24. 3 ZnO 15. 9

"In Table 5 are given examples of glasses which besides 3. The optical glass of claim 2 in which the oxide of barium lactate and zinc borate have additions of calcium the group consisting of magnesium and calcium is added borate, zinc oxide, zirconium oxide, silica, tungsten oxide, as a metaborate in amount up to by weight of the lead oxide and aluminum oxide. entire mixture.

Table 5 in percent by weight Melt N Br/Iv 79 Br/Iv/s2 Br IV170 Br/IV/71 Br/IV/72 Br/IV/73 Brim/74 Br/l'V/75 Br/IV/76 Br/rvlsn Br/IV/Sl 0&(BO2)9. 19.5 20.3 39. 33.1 37.2 37.2 37.2 17.8 Ba(BO2)2. e 32. 2 33. 4 13. 13. 5 .13. 1 13. 1 13. 1 29. 2 Zn(B 002... 29. 2 '25. 4 24. 7 24. 7 24. 7 25. 6 ZnO 2. 2 2.1 2.1 2.1 3. 4 7.0 6.8 6.8 6.8 6.7 8.8 8.6 8.6 a6 3.4 2.7 2.6 2.6 2.3 4.9 4.9 3.9 69 2.6 1.663 1.672 1.652 1.661 1 642 1.675 1 685 5.7 50. 3 53.4 51. 5 54 2 50. 2 47 8 Instead of'calcium b'orate 'mag'nesium'jborate can be 4. Optical glass of claim 3 molten from a mass which used either entirely or in part and for barium strontium consists essentially of-the borates of the group consisting borate can be used-either entirely or in part. If instead of barium and strontium, of the group consisting of zinc of zinc borate or zinc oxide, cadmium borate or cadmium and cadmium and of borates of the group consisting of oxidebe substituted in part or entirely the index of remagnesium and calcium in which the portions of the fraction can be raised substantially at the expense of the several borates lie within the following limits: dispersion.

Technically known minor additions for further stabiliz- 40 Sr and Ba group Pemzm by 2 5 ing, as aluminum oxide and the like, or additions for Zn and Cd gro'up 204,0 decolorizing, as arsenic oxide and additions which fiacili- Mg and Ca g'f 1040 tate melting such as small additions of alkali Oxides 0r cryolite, lie within the field of the above invention, and the sum of the borates amounts to between 70% and The mixtures are suitably melted down in platinum 85% by W g of the lxtllr vessels: the temperature adjusts itself essentially to the Optlcal iglflss of 015F111 1 111 Whleh p 15% y zirconium compound or silica content respectively. With Welgllt z 1S Present the F a high content of zirconium and silica it must be refined p 1ca l glass of Claim 1 111 which up to 15% by at 1400 C. The cooling down and casting of the melts Weight of 1 2 18 Present the P does not exceed the known technical practice. 7. Optical glass of claim 1 in which up to 20% by Having described our invention, Whatwe claim is: weight of PbOis present in the melt. 1. Optical glass molten from a mixture consisting essen- 8. Optical glass of claim 1 in which index of refracy of at least 0118 OXide 0f the group of elements contion controls are present in the glass, said controls con- Sisting of barium and Strontium, at least one oxide of the sisting of at least one member of thegroup consisting of group of elements consisting of zinc and cadmium, and 0 m 5% by Weight and p o up to 10% by Weight boric oxide in which the amount of boric oxide is present Optical glass of claim 1 in which the mglt is stab in amount to form borates of the oxides of the groups and bilized by the addition of A1203 up to 10% by Weight. in which the mol ratio of the-oxide of the group consisting ot'barium and strontium to the'oxide of the group References Cited in the fil f this patent consisting of zinc and cadmium is between 1.5 and 0.2.

2.1116 optical'glass of claim l'in'which an oxide of V UNITED STATES PATENTS the group consisting of magnesium and calcium is added. I 2,764,492 Weissenberge et a1. Sept. 25, 1956 

1. OPTICAL GLASS MOLTEN FROM A MIXTURE CONSISTING ESSENTIALLY OF AT LEAST ONE OXIDE OF THE GROUP OF ELEMENTS CONSISTING OF BARIUM AND STRONTIUM, AT LEAST ONE OXIDE OF THE GROUP OF ELEMENTS CONSISTING OF ZINC AND CADMIUM, AND BORIC OXIDE IN WHICH THE AMOUNT OF BORIC OXIDE IS PRESENT IN AMOUNT TO FORM BORATES OF THE OXIDES OF THE GROUPS AND IN WHICH THE MOL RATIO OF THE OXIDE OF THE GROUP CONSISTING OF BARIUM AND STRONTIUM TO THE OXIDE OF THE GROUP CONSISTING OF ZINC AND CADMIUM IS BETWEEN 1.5 AND 0.2. 